Self-sacrifice-template epitaxial growth of hierarchical MnO@NiCoO heterojunction electrode for high-performance asymmetric supercapacitor.

Constructing three-dimensional (3D) hierarchical bimetallic pseudocapacitive materials with abundant opening channel and heterojunction structures is rather promising but still challenging for high-performance supercapacitors. Herein, a self-sacrifice-template epitaxial growth strategy was proposed for the first time to construct 3D hierarchical bimetallic pseudocapacitive material. By using this strategy, NiCoO nanowires (NiCoONW) arrayed randomly to form a porous shell via in-situ epitaxial growth fully enclosing a MnO tube core, forming multiple transport channels and nano-heterojunctions between MnO and NiCoONW, which facilitates electron transfer, i.e. exhibiting high electronic conductivity than any single component. As a result of the self-sacrifice-template epitaxial growth method, special hollow tectorum-like 3D hierarchical structure with considerable inter-nanowire space and hollow interior space enables easy access of electrolyte to NiCoONW surface and MnO core, thereby resulting in highly exposed redox active sites of MnO core and NiCoONW shell for energy storage. Comprehensive evaluations confirmed MnO@NiCoONW was a supercapacitor electrode candidate, delivering a superior energy density of 106.37 Wh kg. Such performance can be ascribed to the synergistic coupling effect of 3D hierarchical tube and nano-heterojunction structures. The proposed self-sacrifice-template epitaxial growth strategy provides important guidance for designing high-performance energy storage materials.